1. Field of the Invention
The present invention relates to a digital signal editing apparatus and method which can preferably be employed when editing and displaying a moving image signal and an acoustic signal recorded on a storage medium which allows random access such as a magneto-optical disc.
2. Description of the Related Art
FIG. 1 shows configuration of a digital signal editing system for editing at least one coded data string recorded on a storage medium which allows random access such as an optical disc.
A coded data constituting said coded data string recorded in a storage medium 31 is reproduced by a reproduction apparatus 32 whose reproduction timing is controlled by a control unit 33, and is displayed on a display unit 34. Whiles the data is displayed on the display unit 34, a portion to be edited is determined by an editor.
The control unit 33, after moving a read position of the storage medium 31 up to the portion to be edited, makes the reproduction apparatus 32 start reproduction of a signal. The control unit 33 also controls the recording timing of the recording apparatus 35. When the reproduction apparatus 32 starts reproduction of a signal, the signal is recorded on another recording medium 36 in the recording apparatus 35.
For this, the reproduction apparatus 32 and the recording apparatus 35 should be synchronized for operation. This synchronization is controlled by a signal from the control unit 33. Note that a signal transmitted from the reproduction apparatus 32 to the recording apparatus 35 is a coded signal which has been decoded or not. When a decoded signal is transmitted from the reproduction apparatus 32 to the recording apparatus 35, the reproduction apparatus 32 decodes by a decoder a coded data from the storage medium 31, so as to be transmitted to the recording apparatus 35, which receives the decoded signal and codes the signal, which is recorded on the storage medium 36.
FIG. 2 shows configuration of a digital signal editing system for carrying out a nonlinear edition. A data recorded on a storage recording medium 40 having a large capacity such as a magnetic tape is reproduced by a recording/reproduction apparatus 41 and read out to a storage unit 43 which allows random access such as a hard disc drive (HDD) connected to an editing unit 43. This storage unit 43 may be built in the editing unit 42. A data which is read out here is a coded data or an original signal such as an image/sound signal or the like according to the configuration of the editing system.
An editor, while checking the image/sound signal on a display unit 44, edits a data in the storage unit 43 by the editing unit 42 and records the edited data in the storage unit 40 by using the recording/reproduction apparatus 41. As this editing unit 42, a personal computer and a work station may be used. In such a case, the storage unit 43 may be an HDD or RAM connected to (or built in) the computer.
It is possible to increase the editing efficiency by reading a data into the storage unit 43 allowing random access, but it is necessary that a data be read from the storage medium 40 into the storage unit 43 and, after edition is complete, the data should be written back into the aforementioned storage medium 40. In the same way as the example of FIG. 1, the system of FIG. 2 requires a reproduction process and a recording process.
A typical editing operation using the editing system shown in FIG. 1 and FIG. 2 will be explained below with reference to FIG. 3. FIG. 3A shows a part of data D1 to be deleted and the data D0 preceding the deleted data is connected to the data D2 following the deleted data. This operation will be referred to as a skip edition.
FIG. 3B shows a data divided at point PA into a data part D0 and a data part D1, between which another data part D2 is inserted. This editing operation will be referred to as an insert edition.
FIG. 3C shows a data part D1 replaced by another data D3. This operation will be referred to as a replacement edition.
Recently, in a system for recording an image signal and a sound signal on a recording medium such as an optical disc and a magnetic tape and reproducing the signal on a display unit, or in a video conference system or a visual telephone system in which an image signal and a sound signal are transmitted from a transmission side via a predetermined transmission path so as to be displayed at a reception side, these image and sound signals, after A/D conversion, are often subjected to coding by the MPEG (Moving Picture Experts Group) method for compressing a data amount.
Here, the MPEG is an abbreviation of a working group for moving image coding for storage, which belongs to ISO/IEC JTC1/SC29 (International Organization for Standardization/International Electrotechnical Commission, Joint Technical Committee 1/Sub Committee 29). There are ISO11172 as the MPEG1 standard, and ISO13818 as the MPEG2 standard. In these international standards, there are ISO11172-1 and ISO13818-1 for system multiplexing; ISO11172-2 and ISO13818-2 for image coding; and ISO11172-3 and ISO13818-3 for sound coding.
In order to code an image with a high efficiency and to realize random access, the MPEG provides three coding types: I picture, B picture, and P picture. Here, the term xe2x80x98picturexe2x80x99 represents a coded screen (frame or field) constituting a moving image.
The I picture is a data for which coding is complete in the aforementioned screen and is coded independently of another screen. Consequently, the I picture is used as an entry point for random access and error recovery. However, if the frequency of the I picture becomes high, the coding efficiency is lowered.
The P picture means a mode for carrying out forward predictive coding and is predicted from an I picture or P picture which is temporally in the past. Consequently, in order to decode a P picture, it is necessary that the preceding I picture or P Picture have been decoded. By using the P picture, the coding efficiency is increased in comparison with a case when carrying out coding only using the I picture.
The B picture is an advanced step of the P picture and provides a mode for carrying out predictive coding in both directions, i.e., by using I pictures or P pictures of the past and the future, prediction is carried out in a forward direction, a backward direction, or in both directions. Consequently, in order to decode a B picture, the preceding and the following I picture or P picture should have been decoded. By introducing this B picture, the coding efficiency is significantly improved.
In general, an ordinary application employs the aforementioned I, B, and P pictures in combination so as to obtain random access and a high coding efficiency.
FIG. 4A shows an example of such combination. In this FIG. 4A, the aforementioned screens (pictures) are arranged in the display order. In this FIG. 4A, each of the arrows indicates a prediction direction. For example, when a B picture is to be decoded for display, the preceding and the following (temporally) I picture or P picture should be decoded prior to decoding the B picture.
More specifically, in a case when realizing the display order of the aforementioned FIG. 4A, in order to decode an image of the picture B5, at least pictures I0, P2, P4, and P6 should be decoded in advance. That is, the picture P2 is predicted from the picture I0; the picture P4 is predicted from the picture P2; the picture P6 is predicted from the picture P4; and the picture B5 is predicted from the pictures P4 and P6. Consequently, in order to decode the picture B5, the pictures I0, P2, P4, and P6 should be decoded in advance.
Therefore, as shown in FIG. 4B, these pictures are arranged in the coded stream in the order of I0, P2, B11, P4, B3, . . . In other words, the coded stream of pictures as shown in FIG. 4B is recorded on the recording medium. Consequently, when reproducing this recording medium for display an image on a display unit, the pictures are decoded from the coded stream reproduced from the recording medium and they are re-arranged as shown in FIG. 4A for display.
In the so-called CD and DVD (digital versatile disc) which have been normalized and introduced on market, an image is coded by the MPEG method having the aforementioned configuration and a sound is coded by the MPEG or AC-3 (ATSC standard DOC.A/52, Dec. 20, 1995) method. These data are time division multiplexed by the MPEG system specification and recorded on the disc.
When the editing system as shown in FIG. 1 is used for editing an image signal and a sound signal or these signals which have bee multiplexed, it is necessary to provide a reproduction apparatus for reproducing an original signal and a recording apparatus for recording a signal after edition, increasing the size of the entire system.
For example, if it is assumed to carry out edition using a storage medium containing an image signal which has been coded by the aforementioned MPEG method, in order to increase the coding efficiency, the MPEG usually includes a predictive coding mode (i.e., including B pictures and P pictures). Consequently, when carrying out on frame basis, firstly a coded data is read out to be decoded and an image signal obtained is edited and coded again, after which the signal is recorded in a storage medium, thus requiring a large editing system. Moreover, two storage media are required: one containing an original signal coded and the other for recording a data after edition.
Furthermore, in such an editing system, a signal edited is recorded again on another storage medium, which requires a time almost identical to the length of the image edited during edition.
Moreover, in the nonlinear edition as carried out in the editing system shown in FIG. 2, a data is transferred from a storage medium to a storage unit within a editing apparatus and the data after edition is again written into the storage medium, which requires a time for transfer and a storage unit of large capacity for keeping this data.
It is therefore an object of the present invention to provide a digital signal editing apparatus and method which does not require data re-recording after edition and enables to realize an editing system of small size and reduce a time required for edition.
In order to achieve the aforementioned object, in the digital signal editing apparatus according to the present invention, read-out by read-out means is controlled by control means according to a reproduction information on a reproduction interval of a coded data, and this read-out coded data is decoded by decoding means so as to output an edited decoded data string.
Moreover, according to the digital signal editing method according to the present invention, in order to achieve the aforementioned object, a plurality of coded data are read out from a storage medium allowing random access, according to the aforementioned reproduction information on a reproduction interval of the coded data, and the read-out coded data are L decoded so as to be continuous temporally and made into an edited decoded data string.